Diffrential Gearing Replacement

[Nicolas Aristodemou]

I am contemplating the replacement of the crown wheel /bevel gear set in my USA spec 280 SL auto 1970, which I believe has either a 4.08 or a 3.92 differential, probably the former, since I am cruising in top gear at 60mph at about 3250rpm. I am going for a 3.46 ratio which I hope will give me a much more quiet ride since I am using the car for relaxed highway cruising.

I will leave this job to a specialist shop in Germany, where I am sourcing the new gears from, who at the same time will replace any bearings and seals as necessary, but more importantly set the gears properly inside the diff.

My question is what will happen to the speedometer and more importantly odometer of the car. At present they are both spot on and have amazing accuracy. I know that a speedometer can easily be recalibrated by specialists but what about the odometer? It would presumably require new gears with different number of teeth etc and I do not know if these parts are available and if this odometer exercise has been done successfully by anyone before. I think diffs with these ratios were originally fitted to W109s but don't know if these odometer gears would fit into the W113's odometer.

Any help is appreciated, thanks, Nicolas 

[ja17]

Yes the speedometer can be re-calibrated to your new gearing so it will remain accurate. Many good speedometer specialists can do this for you. There is a simple process of measuring distance and counting wheel revolutions that you must record after the diff gearing is changed. Some owners have sources for a speedometer cable miniature gear reduction box which hooks in-line on the speedometer cable to recalibrate the speedometer.

[Nicolas Aristodemou]

Thanks Joe, I will see what I can do after the diff transplant is completed. Maybe I will also source parts (odometer gears) from an 109 speedometer that had an identical diff ratios. I think I have access to such a unit left at my electrician's shop years ago....

I will keep this forum posted if I am successful. First I will have to get on with the transplant..... Not an easy job....

[teahead]

Where can you get 3.46 gears?

[Nicolas Aristodemou]

Yes I have found a supplier in ebay, sells them for 1500 euro

[teahead]

Yes I have found a supplier in ebay, sells them for 1500 euro

This guy?

https://www.ebay.de/itm/Tellerrad-Kegelrad-Satz-1-3-46-fur-Mercedes-W108-W109-W113-Hinterachse/401796617979?hash=item5d8cf1d6fb:g:~K4AAOSwdkNd6OxR

Seems like it's be easier and more usable to do the Getrag 265 swap.

[Nicolas Aristodemou]

yes that's them...... I haven't ordered yet, I need to clarify few things about the logistics of the transplant of the crown and pinion with a specialist in Germany first.....